1. Field of the Invention
The invention relates to a method for a hybrid automatic repeat request. More particularly, the invention relates to a method for an end-to-end hybrid automatic repeat request and a system thereof used in cognitive radio networks of multi-hop relay.
2. Description of Related Art
Cognitive radio network (CRN) technology is used to improve a spectrum utilization efficiency of wireless communication. Each node in the CRN can detect whether or not neighbouring nodes in a primary wireless network having a licensed wireless spectrum are using the licensed wireless spectrum, and transmit data to the other neighbouring nodes in the CRN by using a time slot in which the neighbouring nodes in the primary wireless network do not use the licensed wireless spectrum. Accordingly, a transmission throughput can be effectively increased in a given bandwidth by using the CRN, and therefore the spectrum utilization efficiency can be relatively improved.
However, in the CRN, one or a plurality of multi-hop relay paths is required for transmitting packets from a source node to a destination node, and each one of the multi-hop relay paths has a plurality of uni-directional opportunistic wireless links. Each uni-directional opportunistic wireless link in each one of the multi-hop relay paths can just guarantee to obtain a uni-directional transmission opportunity, but cannot guarantee a transmission opportunity of an opposite direction. Therefore, the link of the CRN is lack of an error control mechanism in a link layer (level) and also lack of an automatic repeat transmission mechanism in the link layer (level), which is developed with the assumption of link bi-directionality.
Accordingly, assuming the destination node in the CRN detects an error of a received packet, by using a conventional automatic repeat request in link layer (level), the destination node cannot feedback the negative acknowledgment to the source node since the link is uni-directional. Therefore, efficient operation of the CRN cannot be achieved, and the transmission throughput and the spectrum utilization efficiency cannot be improved.